This disclosure relates generally to hoists. More particularly, this disclosure relates to rescue hoists for aircraft.
Rescue hoists deploy and retrieve a cable from a cable drum to hoist persons or cargo, and the rescue hoist may be mounted to an aircraft, such as a helicopter. The rescue hoist includes a drum off of which the cable is deployed. The cable drum rotates to spool or unspool the cable from the cable drum, with one end of the cable attached to the cable drum and the other end, which can include a hook or other device, deployed during operation. The length of cable that is currently deployed is an important parameter for the user to know during operation of rescue hoists. A deployment sensor is employed to determine the number of rotations of the cable drum, and a control system can calculate the deployed length based on the sensed number of rotations. Multi-turn transducers can directly sense the number of rotations, but a multiple turn transducer does not maintain the positional reading if power is lost. Single-turn transducers typically require complex planocentric drives or a bulky arrangement having multiple stages of gear reduction to achieve the high gear ratios required by the single-turn transducer.